Flat roofs require more maintenance than do sloped roofs because debris tends to collect on them. But they're safer to walk on than sloped roofs. As long as you're careful not to damage the roofing material as you work, it's easy to keep them functional. Bruce O'Neal of Matthews Roofing in Chicago says keeping drains and scuppers clear is the single-most-important maintenance task, because backups there will trap standing water on the roof. Fall is a good time to sweep off leaves and dirt that would turn into mulch over the winter. "We've seen trees growing out of poorly maintained roofs," says O'Neal. Trees on the ground are a problem too. "Low branches that could scrape the roof should be removed before they cause damage," he says. He also advises checking the flashing for cracked caulking, which can be easily removed and replaced. Large cracks or splits in a flat roof probably need professional attention, but small punctures or worn spots often can be mended using home-center patch kits for your type of roof. On rubber roofs, TOH general contractor Tom Silva patches small holes with a regular bicycle-tire repair kit.